Dielectric ceramic compositions

ABSTRACT

Dielectric ceramic composition consisting essentially of substance selected from those represented by the following formulas: (1) Pba(Mg1/3Nb2/3)xTiy(Ni1/2W1/2)zO2+a (2) PbaCab(Mg1/3Nb2/3)xTiy(Ni1/2W1/2)zO2+a+b (3) PbaBab(Mg1/3Nb2/3)xTiy(Ni1/2W1/2)zO2+a+b (4) PbaSrb(Mg1/3Nb2/3)xTiy(Ni1/2W1/2)zO2+a+b wherein x+y+z=1.00, and a or a+b&gt;/=1.001. These compositions can be sintered below 1080 DEG  C. in low partial pressure of oxygen of about 1x10-8, and exhibit a high dielectric constant and a high electrical resistivity.

BACKGROUND OF THE INVENTION

The present invention relates to dielectric ceramic compositions allowing sintering at low temperature and at low partial pressure of oxygen, and exhibiting a high dielectric constant, high electrical resistivity, low temperature coefficient of the dielectric constant, and low dielectric loss, whereby they are suitable for use as dielectric material for fabricating multi-layer ceramic capacitors having copper metal internal electrodes.

Recently, multi-layer ceramic capacitors have been used widely in electrical circuits of various electrical products, because such capacitance are small and have large capasitance and high reliability.

In general, multi-layer ceramic capacitors especially exhibiting large capacitance have been manufactured by cofiring barium titanate based ceramics as dielectric materials and internal electrode metals in an oxidizing atmosphere at a temperature above 1200° C. However, firing under these conditions necessitates a highly expensive internal electrode metal such as platinum or palladium, because the electrode material used in such a system must not melt and must not be oxidized in the atmosphere at the firing temperature.

Therefore there have still been two demands for dielectric ceramic materials. One demand is to be able to be sintered at a temperature below 1100° C. for enabling the use of relatively cheap metals such as silver-30% palladium for internal electrodes. The other demand is to be able to be sintered in reducing atmospheres and exhibit high specific resistivity for enabling the use of base metals such as nickel or copper.

U.S. Pat. No. 4,115,493 discloses non-reducing dielectric ceramic compositions of [(Ba_(1-x) Ca_(x))O]_(m) (Ti_(1-y) Zr_(y))O₂, which can be sintered at a temperature range of 1300° C. to 1400° C. in an atmosphere of low partial pressure of oxygen, and which exhibit a high electrical resistivity. Since sintering temperature of this system is above 1100° C., nickel metal can be used for an internal electrode in the multi-layer ceramic capacitors employing this composition as dielectric materials, but copper metal cannot be used for that. The electrical conductivity of nickel metal is lower than copper, silver, platinum and palladium, so that when nickel metal is employed as internal electrode, loss factor of the capacitor becomes large especially in high frequency.

U.S. Pat. No. 4,450,240 discloses low temperature sintering ceramic compositions of PbTiO₃ -Pb(Ni_(1/3) Nb_(2/3))O₃ -Pb(Mg_(1/2) W_(1/2))O₃, which can be sintered at a temperature range of 900° C. to 1050° C. in an oxidizing atmosphere. This patent teaches that some complex perovskite compositions containing lead can be sintered at low temperature below 1100° C., and exhibit a high dielectric constant and a high electrical resistivity.

Although silver or silver-palladium metals can be used for internal electrodes in the multi-layer ceramic capacitors employing this composition as dielectric materials, copper metal cannot be used, because this composition can not be sintered in a reducing atmosphere.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a dielectric ceramic composition which can be sintered at a temperature below 1080° C. and in low partial pressure of oxygen, and exhibits a high dielectric constant and a high specific resistivity.

To attain this object, a dielectric ceramic composition according to the present invention essentially consists of a substance selected from those represented by the following formulas:

(1) Pb_(a) (Mg_(1/3) Nb_(2/3))_(x) Ti_(y) (Ni_(1/2) W_(1/2))_(z) O_(2+a)

(2) Pb_(a) Ca_(b) (Mg_(1/3) Nb_(2/3))_(x) Ti_(y) (Ni_(1/2) W_(1/2))_(z) O₂ +a+b

(3) Pb_(a) Ba_(b) (Mg_(1/3) Nb_(2/3))_(x) Ti_(y) (Ni_(1/2) W_(1/2))_(z) O_(2+a+b)

(4) Pb_(a) Sr_(b) (Mg_(1/3) Nb_(2/3))_(x) Ti_(y) (Ni_(1/2) W_(1/2))_(z) O_(2+a+b)

wherein subscripts a, b, x, y and z represent molar fractions of the respective components, x+y+z=1.00, and a or a+b≧1.001.

These novel composition of the present invention can be sintered below 1080° C. in low partial pressure of oxygen about 1×10⁻⁸, and have a high dielectric constant and further have a high electrical resistivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a composition diagram of Pb_(a) TiO_(2+a) -Pb_(a) (Mg_(1/3) -Nb_(2/3))O_(2+a) -Pb_(a) (Ni_(1/2) /W_(1/2))O_(2+a) ternary system composition in accordance with the present invention;

FIG. 2 is a composition diagram of Pb_(a) Ca_(b) TiO_(2+a+b) -Pb_(a) Ca_(b) -(Mg_(1/3) Nb_(2/3))O_(2+a+b) -Pb_(a) Ca_(b) (Ni_(1/2) W_(1/2))O_(2+a+b) ternary system composition in accordance with the present invention;

FIG. 3 is a composition diagram of Pb_(a) Ba_(b) TiO_(2+a+b) -Pb_(a) Ba_(b) -(Mg_(1/3) Nb_(2/3))O_(2+a+b) -Pb_(a) Ba_(b) (Ni_(1/2) W_(1/2))O_(2+a+b) ternary system composition in accordance with the present invention; and

FIG. 4 is a composition diagram of Pb_(a) Sr_(b) TiO_(2+a+b) -Pb_(a) Sr_(b) -(Mg_(1/3) Nb_(2/3))O_(2+a+b) -Pb_(a) Sr_(b) (Ni_(1/2W) _(1/2)) O_(2+a+b) ternary system composition in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The composition herein may be prepared in accordance with various well-known ceramic procedures.

EXAMPLE 1

The starting materials, viz. lead oxide (PbO), titanium oxide (TiO₂), niobium oxide (Nb₂ O₅), magnesium oxide (MgO), nickel oxide (NiO), and tungsten oxide (WO₃), all relatively pure grade, were initially mixed in a ball mill with distilled water and agate balls for 17 hours. Thereafter the mixture was dried and then pressed into columns, and calcined at a temperature in the range of 750° C. to 880° C. for 2 hours in an aluminum crucible. The substance thus obtained was wet ground in a ball mill, dried, mixed with polyvinyl alcohol as a binder solution, and then pressed into disks of about 13 mm in diameter and about 0.8 mm in thickness at a pressure of 1000 Kg/cm², and then the binder was burned out at about 700° C. in air.

The burned out disks were put into a magnesia crucible. Initially about 1/3 of volume fraction of this crucible was filled with calcined powder as mentioned above, at the bottom of the crucible, and coarse zirconia powder was laid upon the calcined powder with about 1 mm thickness. The burned out disks were put upon the coarse zirconia layer. Then a magnesia cover was put on the crucible. This crucible containing specimens was inserted into an aluminum tube in a furnace. After the air in the aluminum tube was exhausted by a rotary pump, N₂ --H₂ --H₂ O mixture gas was flowed into the tubes. The partial pressure of H₂ O in an initial mixture gas was 3.2×10⁻³ atm, and the partial pressure of H₂ in an initial mixture gas was 2.2×10⁻⁴ atm, and the partial pressure of O₂ in a initial mixture gas was 1.0×10⁻⁴ atm.

The specimens were sintered at a temperature in the range of 850° C. to 1100° C. for 2 hours. The partial pressure of oxygen of the atmosphere in the sintering process was measured with yttrium oxide stabilized zirconia O₂ sensor which was inserted on to the magnesia crucible in the aluminium tube. The partial pressure of oxygen of the atmosphere at the sintering temperature was 1.0×10⁻⁸ to 1.0×10⁻¹² atm, which was decreased in accordance with lowering of the sintering temperature.

The sintered bodies were measured for densities. The sintering temperature is selected so that the density of the sintered disks becomes maximum. After measuring the densities Cr-Au electrodes were attached on both surfaces of the disks by a method of vacuum evaporation.

Various properties of the ceramic disks thus obtained are shown in TABLE 1. The dielectric constant (ε) and the dielectric loss (tan δ) were measured at a frequency of 1 KHz and a voltage of 1 V at 20° C. The temperature coefficients of the dielectric constants were obtained by measuring the dielectric constants at temperatures in the range of -25° C. to 85° C. and calculating the dielectric constant at 20° C. The electrical resistivity is measured at 20° C. under application of a D.C voltage of 1000 V.

From TABLE 1 it is obvious that ceramic compositions which fall within the polygon ABCDE in the ternary system composition diagram of FIG. 1 and in which 1.001≦a≦1.110 provide a high dielectric constant (ε=21,350 to 7520), high electrical resistivity up to 1.0×10¹¹ Ω.cm, low dielectric loss, low temperature coefficient of the dielectric constant, and can be sintered below 1080° C.

                                      TABLE 1                                      __________________________________________________________________________                                 Change of        Specific                                          Sintering   ε  tan δ                                                                          resistivity                       Composition     temperature                                                                           ε                                                                           (-25° C.)                                                                     (85° C.)                                                                     (20° C.) ×                                                              (20° C.)                                                                       Density                    No. a  x  y  z  (°C.)                                                                          (20° C.)                                                                     %     %    10.sup.-4                                                                            Ω · cm                                                                 g/cm.sup.3                 __________________________________________________________________________      101*                                                                              1.000                                                                             0.850                                                                             0.100                                                                             0.050                                                                             1080   16860                                                                               -45.2 -61.8                                                                               266   1.0 × 10.sup.+9                                                                 7.653                      102 1.001                                                                             0.850                                                                             0.100                                                                             0.050                                                                             1020   16980                                                                               -44.9 -61.0                                                                               112   1.5 × 10.sup.+11                                                                7.998                      103 1.025                                                                             0.850                                                                             0.100                                                                             0.050                                                                             950    15870                                                                               -44.6 -60.8                                                                                56   2.6 × 10.sup.+12                                                                8.153                      104 1.110                                                                             0.850                                                                             0.100                                                                             0.050                                                                             860    10690                                                                               -40.8 -54.6                                                                               102   1.0 × 10.sup.+12                                                                8.223                       105*                                                                              1.180                                                                             0.850                                                                             0.100                                                                             0.050                                                                             830     6830                                                                               -39.5 -42.3                                                                               305   8.5 × 10.sup.                                                                   8.159                       106*                                                                              1.000                                                                             0.700                                                                             0.200                                                                             0.100                                                                             1050   20390                                                                               -60.0 -54.0                                                                               622   7.5 × 10.sup.+9                                                                 7.865                      107 1.001                                                                             0.700                                                                             0.200                                                                             0.100                                                                             1020   21340                                                                               -60.0 -53.4                                                                               422   5.0 × 10.sup.+11                                                                7.963                      108 1.025                                                                             0.700                                                                             0.200                                                                             0.100                                                                             920    20630                                                                               -60.0 -52.6                                                                               432   1.6 × 10.sup.+12                                                                8.122                      109 1.110                                                                             0.700                                                                             0.200                                                                             0.100                                                                             890    15630                                                                               -58.4 -50.2                                                                               622   4.5 × 10.sup.+11                                                                8.103                       110*                                                                              1.180                                                                             0.700                                                                             0.200                                                                             0.100                                                                             820     6230                                                                               -45.3 -40.6                                                                               553   2.6 × 10.sup.+9                                                                 8.096                      111 1.025                                                                             0.950                                                                             0.025                                                                             0.025                                                                             1020   10520                                                                                -5.2 -34.0                                                                               358   5.2 × 10.sup.+11                                                                8.169                      112 1.025                                                                             0.850                                                                             0.125                                                                             0.025                                                                             1020   16090                                                                               -65.4 -26.3                                                                               420   5.0 × 10.sup.+11                                                                8.115                      113 1.025                                                                             0.100                                                                             0.600                                                                             0.300                                                                             880     7860                                                                               -32.6 -51.3                                                                               265   1.5 × 10.sup.+11                                                                8.065                      114 1.025                                                                             0.100                                                                             0.400                                                                             0.500                                                                             860     7520                                                                                +8.6 -60.3                                                                                24   2.5 × 10.sup.+11                                                                8.066                      115 1.025                                                                             0.900                                                                             0.025                                                                             0.075                                                                             950    10890                                                                               -10.6 -60.2                                                                                 36  1.0 × 10.sup.+11                                                                8.104                       116*                                                                              1.025                                                                             0.400                                                                             0.500                                                                             0.100                                                                             900     3220                                                                               -82.5 +40.2                                                                               558   1.0 × 10.sup.+11                                                                8.100                       117*                                                                              1.025                                                                             0.400                                                                             0.200                                                                             0.400                                                                             820     2150                                                                               +25.3 -50.3                                                                               123   1.0 × 10.sup.+11                                                                8.114                      __________________________________________________________________________      (1) Basic compositions: Pb.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y        (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a                                         (2) Compositions of the Nos. with asterisk (*) are outside of the scope o      the present invention.                                                   

A, B, C, D and E of FIG. 1 are represented by the values of x, y, and z as follows:

    ______________________________________                                         x                  y      z                                                    ______________________________________                                         A:      0.950          0.025  0.025                                            B:      0.850          0.125  0.025                                            C:      0.100          0.600  0.300                                            D:      0.100          0.400  0.500                                            E:      0.900          0.025  0.075                                            ______________________________________                                    

The reasons for the limitations of values in TABLE 1 and value <a> are as follows:

In case of the compositions wherein proportions x, y and z are out of the polygon ABCDE such as sample Nos. 116 and 117, the dielectric constant is lower than 3500 and the temperature coefficient of the dielectric constant is large. In case of the compositions wherein a is smaller than 1.001 such as samples Nos. 101 and 106, the electrical resistivity is lower than 1.0×10¹⁰ Ω.cm. In case of the compositions wherein a is larger than 1.110 such as sample Nos. 105 and 110, the dielectric loss are increased.

EXAMPLE 2

The starting materials, viz. lead oxide (PbO), titanium oxide (TiO₂), niobium oxide (Nb₂ O₅), magnesium oxide (MgO), nickel oxide (NiO), tungsten oxide (WO₃), and calcium carbonate (CaCO₃), all relatively pure grade, were initially mixed in a ball mill with distilled water and calcium oxide stabilised zirconia balls for 17 hours. The following powder process, sintered process and measuring of properties of sintering body were the same as those in Example 1.

Various properties of the ceramic disks thus obtained are shown in TABLE 2.

From TABLE 2 it is obvious that ceramic compositions which fall within the polygon FGHIJ in the ternary system composition diagram of FIG. 2 and in which 0.001≦b≦0.225 and 1.001≦a+b≦1.225 provide a high dielectric constant (ε=21540 to 4030), high electrical resistivity up to 1.0×10¹⁰ Ω.cm, low dielectric loss, low temperature coefficient of the dielectric constant, and can be sintered below 1080° C.

F, G, H, I and J of FIG. 2 are represented by the values of x, y and z as follows:

    ______________________________________                                         x                  y      z                                                    ______________________________________                                         F:      0.950          0.049  0.001                                            G:      0.750          0.249  0.001                                            H:      0.010          0.800  0.190                                            I:      0.010          0.450  0.540                                            J:      0.900          0.050  0.050                                            ______________________________________                                    

                                      TABLE 2                                      __________________________________________________________________________                                      Change of        Specific                                          Sintering   ε  tan δ                                                                          resistivity                  Composition          temperature                                                                           ε                                                                           (-25° C.)                                                                     (85° C.)                                                                     (20° C.)                                                                      (20° C.)                                                                        Density              No. a  b   x  y   z  (°C.)                                                                          (20° C.)                                                                     %     %    10.sup.-4                                                                            Ω ·                                                                     g/cm.sup.3           __________________________________________________________________________      201*                                                                              1.000                                                                             0.000                                                                              0.700                                                                             0.250                                                                              0.050                                                                             1120   15390                                                                               -72.6 -50.1                                                                               412   1.5 × 10.sup.+9                                                                  7.661                202 1.000                                                                             0.001                                                                              0.700                                                                             0.250                                                                              0.050                                                                             1050   16320                                                                               -70.2 -50.1                                                                               442   2.0 × 10.sup.+11                                                                 7.891                203 1.000                                                                             0.025                                                                              0.700                                                                             0.250                                                                              0.050                                                                             980    21540                                                                               -52.3 -58.6                                                                               215   8.0 × 10.sup.+13                                                                 8.112                204 1.000                                                                             0.225                                                                              0.700                                                                             0.250                                                                              0.050                                                                             920    14260                                                                               -23.5 -65.3                                                                                42   1.5 × 10.sup.+13                                                                 8.023                 205*                                                                              1.000                                                                             0.400                                                                              0.700                                                                             0.250                                                                              0.050                                                                             950     8500                                                                               + 10.3                                                                               -48.6                                                                               125   4.5 × 10.sup.+12                                                                 7.756                 206*                                                                              0.950                                                                             0.030                                                                              0.700                                                                             0.250                                                                              0.050                                                                             1150   15230                                                                               -58.6 -47.6                                                                               321   5.5 × 10.sup.+9                                                                  7.752                207 0.950                                                                             0.070                                                                              0.700                                                                             0.250                                                                              0.050                                                                             980    16840                                                                               -32.1 -65.3                                                                                32   1.0 × 10.sup.+14                                                                 8.116                 208*                                                                              0.950                                                                             0.350                                                                              0.700                                                                             0.250                                                                              0.050                                                                             950     4860                                                                               -63.2 -32.1                                                                               421   1.6 × 10.sup.+12                                                                 7.985                209 1.035                                                                             0.025                                                                              0.700                                                                             0.250                                                                              0.050                                                                             920    20650                                                                               -50.6 -50.3                                                                               215   8.5 × 10.sup.+13                                                                 8.154                 210*                                                                              1.035                                                                             0.250                                                                              0.700                                                                             0.250                                                                              0.050                                                                             880     4180                                                                               +21.3 -42.5                                                                                23   4.0 × 10.sup.+12                                                                 7.798                 211*                                                                              1.000                                                                             0.000                                                                              0.450                                                                             0.400                                                                              0.150                                                                             1080    9520                                                                               -85.4 -15.2                                                                               542   2.0 × 10.sup.+9                                                                  7.554                212 1.015                                                                             0.001                                                                              0.450                                                                             0.400                                                                              0.150                                                                             1000   10230                                                                               -78.3 -22.4                                                                               512   3.5 × 10.sup.+12                                                                 7.985                213 1.015                                                                             0.025                                                                              0.450                                                                             0.400                                                                              0.150                                                                             920    11560                                                                               -56.3 -41.3                                                                               224   1.5 × 10.sup.+13                                                                 8.087                214 1.000                                                                             0.075                                                                              0.450                                                                             0.400                                                                              0.150                                                                             900    11650                                                                               -41.3 -52.3                                                                                42   4.5 × 10.sup.+13                                                                 8.102                 215*                                                                              1.000                                                                             0.275                                                                              0.450                                                                             0.400                                                                              0.150                                                                             880     2350                                                                               +12.0 -42.3                                                                               145   1.5 × 10.sup.+12                                                                 7.795                216 1.015                                                                             0.025                                                                              0.950                                                                             0.049                                                                              0.001                                                                             920    11860                                                                               -22.3 -82.5                                                                               163   5.0 × 10.sup.+12                                                                 7.858                217 1.015                                                                             0.025                                                                              0.750                                                                             0.249                                                                              0.001                                                                             920     8560                                                                               -85.3 -12.6                                                                               482   3.5 × 10.sup.+12                                                                 7.985                218 1.015                                                                             0.025                                                                              0.010                                                                             0.800                                                                              0.190                                                                             880     4030                                                                               -52.1  -5.3                                                                               662   2.5 × 10.sup.+12                                                                 7.854                219 1.015                                                                             0.025                                                                              0.010                                                                             0.450                                                                              0.540                                                                             850     4250                                                                                +0.8 -41.3                                                                                88   5.0 × 10.sup.+12                                                                 7.965                220 1.015                                                                             0.025                                                                              0.900                                                                             0.050                                                                              0.050                                                                             900    11280                                                                               -22.3 -82.9                                                                                41   4.5 × 10.sup.+12                                                                 8.085                 221*                                                                              1.015                                                                             0.025                                                                              0.300                                                                             0.650                                                                              0.050                                                                             950     1950                                                                               -32.5 +15.3                                                                               253   1.5 × 10.sup.+12                                                                 8.025                 222*                                                                              1.015                                                                             0.025                                                                              0.300                                                                             0.250                                                                              0.450                                                                             900     1480                                                                               +12.3 -45.6                                                                               554   2.5 × 10.sup.+12                                                                 8.152                __________________________________________________________________________      (1) Basic compositions: Pb.sub.a Ca.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x        Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+b                              (2) Compositions of the Nos. with asterisk (*) are outside of the scope o      the present invention.                                                   

The reasons for limitations of values in TABLE 2 and values <a> and <a+b> are as follows:

In case of the compositions wherein proportion x, y and z are out of the polygon FGHIJ such as sample Nos. 221 and 222, the dielectric constant is lower than 3500 and the temperature coefficient of the dielectric constant is large. In case of the compositions wherein b is smaller than 0.001 and a+b is smaller than 1.00 such as sample Nos. 201, 206, and 211, the electrical resistivity are lower than 1.0×10¹⁰ Ω.cm. In case of the composition wherein b is larger than 0.225 and a+b is larger than 1.250 such as sample No. 205, 208, 210, 215, the dielectric constants is decreased or dielectric loss are increased.

EXAMPLE 3

The starting materials, viz. lead oxide (PbO), titanium oxide (TiO₂), niobium oxide (Nb₂ O₅), magnesium oxide (MgO), and nickel oxide (NiO) were initially mixed in a ball mill with distilled water and calcium oxide stabilised zirconia balls for 17 hours. The following power process, sintering process and measuring of properties of sintering body were the same as those in Example 1.

Various properties of the ceramic disks thus obtained are shown in Table 3.

                                      TABLE 3                                      __________________________________________________________________________                                      Change of        Specific                                          Sintering   ε  tan δ                                                                          resistivity                  Composition          temperature                                                                           ε                                                                           (-25° C.)                                                                     (85° C.)                                                                     (20° C.)                                                                      (20° C.)                                                                        Density              No. a  b   x  y   z  (°C.)                                                                          (20° C.)                                                                     %     %    10.sup.-4                                                                            Ω ·                                                                     g/cm.sup.3           __________________________________________________________________________      301*                                                                              1.000                                                                             0.000                                                                              0.700                                                                             0.250                                                                              0.050                                                                             1120   15390                                                                               -72.6 -50.1                                                                               412   1.5 × 10.sup.+9                                                                  7.661                302 1.000                                                                             0.001                                                                              0.700                                                                             0.250                                                                              0.050                                                                             1050   16410                                                                               -70.3 -50.5                                                                               412   1.5 × 10.sup.+11                                                                 7.891                303 1.000                                                                             0.025                                                                              0.700                                                                             0.250                                                                              0.050                                                                             990    18660                                                                               -41.3 -61.2                                                                               111   5.0 × 10.sup.+13                                                                 8.005                304 1.000                                                                             0.200                                                                              0.700                                                                             0.250                                                                              0.050                                                                             920    12260                                                                               -11.2 -78.6                                                                                52   1.0 × 10.sup.+13                                                                 7.923                 305*                                                                              1.000                                                                             0.400                                                                              0.700                                                                             0.250                                                                              0.050                                                                             950     4250                                                                               + 25.3                                                                               -98.3                                                                               585   1.2 × 10.sup.+11                                                                 7.655                 306*                                                                              0.950                                                                             0.030                                                                              0.700                                                                             0.250                                                                              0.050                                                                             1180   13200                                                                               -54.6 -92.6                                                                               445   1.5 × 10.sup.+8                                                                  7.521                307 0.950                                                                             0.070                                                                              0.700                                                                             0.250                                                                              0.050                                                                             1020   14150                                                                               -41.8 -72.2                                                                                25   1.5× 10.sup.+13                                                                  8.008                 308*                                                                              0.950                                                                             0.350                                                                              0.700                                                                             0.250                                                                              0.050                                                                             980     3820                                                                               -70.0 -41.2                                                                               552   1.0 × 10.sup.+11                                                                 7.885                309 1.035                                                                             0.025                                                                              0.700                                                                             0.250                                                                              0.050                                                                             950    17450                                                                               -45.3 -51.2                                                                               125   6.0 × 10.sup.+13                                                                 8.022                 310*                                                                              1.035                                                                             0.200                                                                              0.700                                                                             0.250                                                                              0.050                                                                             880     3820                                                                               +11.7 -78.6                                                                                42   1.0 × 10.sup.+11                                                                 7.665                 311*                                                                              1.000                                                                             0.000                                                                              0.450                                                                             0.400                                                                              0.150                                                                             1080    9520                                                                               -85.4 -15.2                                                                               542   2.0 × 10.sup.+9                                                                  7.554                312 1.015                                                                             0.001                                                                              0.450                                                                             0.400                                                                              0.150                                                                             1000   10450                                                                               -76.2 -21.4                                                                               458   3.5 × 10.sup.+12                                                                 7.885                313 1.015                                                                             0.025                                                                              0.450                                                                             0.400                                                                              0.150                                                                             940    10060                                                                               -43.5 -31.2                                                                               123   1.0 × 10.sup.+12                                                                 8.002                314 1.000                                                                             0.075                                                                              0.450                                                                             0.400                                                                              0.150                                                                             920    10020                                                                               -32.2 -62.3                                                                                33   1.0 × 10.sup.+13                                                                 8.025                 315*                                                                              1.000                                                                             0.220                                                                              0.450                                                                             0.400                                                                              0.150                                                                             900     1890                                                                               +11.2 -52.3                                                                               285   5.0 × 10.sup.+11                                                                 7.662                316 1.015                                                                             0.025                                                                              0.950                                                                             0.049                                                                              0.001                                                                             950    12100                                                                               -22.5 -75.5                                                                               102   4.0 × 10.sup.+12                                                                 7.855                317 1.015                                                                             0.025                                                                              0.750                                                                             0.249                                                                              0.001                                                                             950     7250                                                                               -80.2 -11.2                                                                               552   1.2 × 10.sup.+12                                                                 7.855                318 1.015                                                                             0.025                                                                              0.010                                                                             0.800                                                                              0.190                                                                             900     3880                                                                               -54.2  -9.6                                                                               452   1.5 × 10.sup.+12                                                                 7.885                319 1.015                                                                             0.025                                                                              0.010                                                                             0.450                                                                              0.540                                                                             880     3860                                                                               +12.2 -51.2                                                                                11   2.2 × 10.sup.+12                                                                 7.585                320 1.015                                                                             0.025                                                                              0.900                                                                             0.050                                                                              0.050                                                                             920    10220                                                                               -20.2 -79.3                                                                                22   3.0 × 10.sup.+12                                                                 7.951                 321*                                                                              1.015                                                                             0.025                                                                              0.300                                                                             0.650                                                                              0.050                                                                             980     1560                                                                               -21.2 +11.2                                                                               452   6.0 × 10.sup.+10                                                                 8.001                 322*                                                                              1.015                                                                             0.025                                                                              0.300                                                                             0.250                                                                              0.450                                                                             920     1120                                                                               +22.3 -51.2                                                                               455   1.2 × 10.sup.+11                                                                 8.055                __________________________________________________________________________      (1) Basic compositions: Pb.sub.a Ba.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x        Ti.sub.y (Ni.sub.1/2 W.sub. 1/2).sub.z O.sub.2+a+b                             (2) Compositions of the Nos. with asterisk (*) are outside of the scope o      the present invention.                                                   

From TABLE 3 it is obvious that ceramic compositions which fall within the polygon KLMNO in the ternary system composition diagram of FIG. 3 and in which 0.001≦b≦0.200 and 1.001≦a+b≦1.200 provide a high dielectric constant (ε=18660 to 3860), and high electrical resistivity up to 1.0×10¹⁰ Ω.cm, low dielectric loss and low temperature coefficient of the dielectric constant, and can be sintered below 1080° C.

K, L, M, N and O of FIG. 3. are represented by the values of x, y and z as follows:

    ______________________________________                                         x                  y      z                                                    ______________________________________                                         K:      0.950          0.049  0.001                                            L:      0.750          0.249  0.001                                            M:      0.010          0.800  0.190                                            N:      0.010          0.045  0.540                                            O:      0.900          0.050  0.050                                            ______________________________________                                    

The reasons for limitations of values in TABLE 3 and values <a> and <a+b> are as follows:

In case of the compositions wherein proportion x, y and z are out of the polygon FGHIJ such as sample Nos. 321 and 322, the dielectric constant is lower than 3500 and the temperature coefficient of the dielectric constant is large. In case of the compositions wherein b is smaller than 0.001 and a+b is smaller than 1.00 such as sample Nos. 301, 306 and 311, the electrical resistivity is lower than 1.0×10¹⁰ Ω.cm. In case of the composition wherein b is larger than 0.250 and a+b is larger than 1.200 such as sample Nos. 305, 308, 310 and 315, the dielectric constants are decreased or dielectric loss is increased.

EXAMPLE 4

The starting materials, viz. lead oxide (PbO), titanium oxide (TiO₂), niobium oxide (Nb₂ O₅), magnesium oxide (MgO), nickel oxide (NiO), tungsten oxide (WO₃), and strontium carbonate (SrCO₃), all relatively pure grade, were initially mixed in a ball mill with distilled water and calcium oxide stabilised zirconia balls for 17 hours. The following powder process, the sintered process and measuring of properties of sintering body were the same as those in Example 1.

Various properties of the ceramic disks thus obtained are shown in TABLE 4.

From TABLE 4 it is obvious that ceramic compositions within the polygon PQRS in the ternary system compositions diagram of FIG. 4 and in which 0.001≦b≦0.225 and 1.001≦a+b≦1.240 provide a high dielectric constant (ε=16630 to 4010), high electrical resistivity up to 1.0×10¹⁰ Ω.cm, low dielectric loss and low temperature coefficient of the dielectric constant, and can be sintered below 1080° C.

                                      TABLE 4                                      __________________________________________________________________________                                      Change of        Specific                                          Sintering   ε  tan δ                                                                          resistivity                  Composition          temperature                                                                           ε                                                                           (-25° C.)                                                                     (85° C.)                                                                     (20° C.)                                                                      (20° C.)                                                                        Density              No. a  b   x  y   z  (°C.)                                                                          (20° C.)                                                                     %     %    10.sup.-4                                                                            Ω ·                                                                     g/cm.sup.3           __________________________________________________________________________      401*                                                                              1.000                                                                             0.000                                                                              0.700                                                                             0.250                                                                              0.050                                                                             1120   15390                                                                               -72.6 -50.1                                                                               412   1.5 × 10.sup.+9                                                                  7.661                402 1.000                                                                             0.001                                                                              0.700                                                                             0.250                                                                              0.050                                                                             1050   16630                                                                               -71.2 -51.2                                                                               402   3.0 × 10.sup.+11                                                                 7.884                403 1.000                                                                             0.025                                                                              0.700                                                                             0.250                                                                              0.050                                                                             1000   15320                                                                               -45.3 -42.2                                                                               125   7.5 × 10.sup.+13                                                                 8.023                404 1.000                                                                             0.225                                                                              0.700                                                                             0.250                                                                              0.050                                                                              920    8520                                                                               -15.2 -72.3                                                                                32   1.0 × 10.sup.+13                                                                 7.855                 405*                                                                              1.000                                                                             0.400                                                                              0.700                                                                             0.250                                                                              0.050                                                                             1000    5220                                                                               + 20.3                                                                               -65.3                                                                               225   1.5 × 10.sup.+12                                                                 7.325                 406*                                                                              0.950                                                                             0.030                                                                              0.700                                                                             0.250                                                                              0.050                                                                             1150   12350                                                                               -42.3 -35.6                                                                               225   7.5 × 10.sup.+10                                                                 7.215                407 0.950                                                                             0.070                                                                              0.700                                                                             0.250                                                                              0.050                                                                             1000   11520                                                                               -40.2 -45.3                                                                               125   1.5 × 10.sup.+14                                                                 8.002                 408*                                                                              0.950                                                                             0.350                                                                              0.700                                                                             0.250                                                                              0.050                                                                             1080    2560                                                                               -24.2 -75.3                                                                               542   5.2 × 10.sup.+13                                                                 7.252                409 1.035                                                                             0.025                                                                              0.700                                                                             0.250                                                                              0.050                                                                              980   11560                                                                               -45.2 -42.3                                                                                45   9.0 × 10.sup.+13                                                                 8.088                 410*                                                                              1.035                                                                             0.250                                                                              0.700                                                                             0.250                                                                              0.050                                                                              880    1980                                                                               +32.1 -31.2                                                                                14   7.0 × 10.sup.+12                                                                 7.425                 411*                                                                              1.000                                                                             0.000                                                                              0.450                                                                             0.400                                                                              0.150                                                                             1080    9520                                                                               -85.4 -15.2                                                                               542   2.0 × 10.sup.+9                                                                  7.554                412 1.015                                                                             0.001                                                                              0.450                                                                             0.400                                                                              0.150                                                                             1000   10020                                                                               -74.3 -22.5                                                                               458   7.2 × 10.sup.+12                                                                 7.985                413 1.015                                                                             0.025                                                                              0.450                                                                             0.400                                                                              0.150                                                                              970    9520                                                                               -42.3 -38.5                                                                               114   1.0 × 10.sup.+13                                                                 8.002                414 1.000                                                                             0.075                                                                              0.450                                                                             0.400                                                                              0.150                                                                              950    8560                                                                               -33.2 -65.2                                                                                 52  3.0 × 10.sup.+13                                                                 7.988                 415*                                                                              1.000                                                                             0.275                                                                              0.450                                                                             0.400                                                                              0.150                                                                              900    2850                                                                               +25.3 -55.9                                                                                78   2.6 × 10.sup.+12                                                                 7.668                416 1.015                                                                             0.030                                                                              0.950                                                                             0.049                                                                              0.001                                                                              970   10580                                                                               -20.3 -79.6                                                                                88   7.0 × 10.sup.+12                                                                 7.756                417 1.015                                                                             0.150                                                                              0.400                                                                             0.591                                                                              0.001                                                                             1050    4990                                                                               -77.3  -5.3                                                                               851   2.0 × 10.sup.+12                                                                 7.668                418 1.015                                                                             0.200                                                                              0.001                                                                             0.900                                                                              0.099                                                                             1000    4000                                                                               -42.6  -8.9                                                                               775   1.5 × 10.sup.+12                                                                 7.566                419 1.015                                                                             0.025                                                                              0.001                                                                             0.600                                                                              0.399                                                                              980    4010                                                                                +5.6 -22.1                                                                               115   2.5 × 10.sup.+12                                                                 7.558                420 1.015                                                                             0.225                                                                              0.150                                                                             0.825                                                                              0.025                                                                             1000    1420                                                                               -42.1 +22.3                                                                               336   2.5 × 10.sup.+12                                                                 7.789                 421*                                                                              1.015                                                                             0.025                                                                              0.150                                                                             0.350                                                                              0.500                                                                              980    2150                                                                               -1.23 -52.1                                                                               335   1.3 × 10.sup.+12                                                                 8.002                __________________________________________________________________________      (1) Basic compositions: Pb.sub.a Sr.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x        Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+b                              (2) Compositions of the Nos. with asterisk (*) are outside of the scope o      the present invention.                                                   

P, Q, R and S of FIG. 4 are represented by the values of x, y and z as follows:

    ______________________________________                                         x                  y      z                                                    ______________________________________                                         P:      0.950          0.049  0.001                                            Q:      0.400          0.591  0.001                                            R:      0.001          0.900  0.099                                            S:      0.001          0.600  0.399                                            ______________________________________                                    

The reasons for limitations of values in FIG. 4 and values <a> and <a+b> are as follows:

In case of the compositions wherein proportion x, y and z is out of the polygon PQRS such as sample Nos. 320 and 321, the dielectric constant is lower than 3500 and the temperature coefficient of the dielectric constant is large. In case of the compositions wherein b is smaller than 0.001 and a+b is smaller than 1.00 such as sample Nos. 301, 306 and 311, the electrical resistivity is lower than 1.0×10¹⁰ Ω.cm. In case of the composition wherein b is larger than 0.250 and a+b is larger than 1.200 such as sample Nos. 305, 308, 310 and 315, the dielectric constants are decreased or dielectric loss are increased.

As apparent from these Examples 1 to 4, the ternary ceramic compositions according to the present invention can be sintered below 1100° C., and in low partial pressure of oxygen atmosphere, at which temperature and atmosphere the copper metal internal electrode is not melted and oxidized, and exhibit high dielectric constant, high electrical resistivity, low dielectric loss and low temperature coefficient of dielectric constant. Therefore copper metal can be used as internal electrodes of multi-layer ceramic capacitors, employing compositions according to this invention as dielectric materials.

It will be evident that the starting materials to be used in the present invention are not limited to those used in the above examples. Other oxides or compounds which are easily decomposed at elevated temperature may be used in place of the starting materials of the above examples. 

What is claimed is:
 1. A ceramic composition consisting essentially of a material represented by the formula

    Pb.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a

wherein subscripts a, x, y and z represent molar fractions of the respective components, x+y+z=1 and 1.001≦a≦1.110, said composition falling within a polygonal area defined by the points A, B, C, D and E in FIG.
 1. 2. A ceramic composition consisting essentially of a material represented by the formula

    Pb.sub.a Ca.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+b

wherein subscripts a, b, x, y and z represent molar fractions of the respective components, x+y+z=1, 1.001≦a+b≦1.225, and 0.001≦b≦0.225, said composition falling within a polygonal area defined by the points F, G, H, I and J in FIG.
 2. 3. A ceramic composition consisting essentially of a material represented by the formula

    Pb.sub.a Ba.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+b

wherein subscripts a, b, x, y and z represent molar fractions of the respective components, x+y+z=1, 1.001≦a+b≦1.200, and 0.001≦b≦0.200, said composition falling within a polygonal area defined by the points K, L, M, N and O in FIG.
 3. 4. A ceramic composition consisting essentially of a material replesented by the formula

    Pb.sub.a Sr.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+b

wherein subscripts a, b, x, y and z represent molar fractions of the respective components, x+y+z=1, 1.001≦a+b≦1.240, and 0.001≦b≦0.225, said composition falling within a polygonal area defined by the points P, Q, R and S in FIG.
 4. 